Total nitrogen (abbreviated as TN) refers to the total amount of inorganic and organic nitrogen in various forms in water, including inorganic nitrogen such as NO3−, NO2− and NH4+, as well as organic nitrogen such as proteins, amino acids and organic amines, and is calculated as milligrams of nitrogen per liter of water. It is often used to indicate the degree to which the water body is contaminated by nutrient substances. When the nitrogen and phosphorus containing substances in the surface water are excessive, microorganism blooms, plankton grows vigorously, and thus eutrophication status occurs.
With regard to the discharge of industrial effluents, different standards for different industries have also been set in our country. For one example, it is stipulated in GB3544-2008 (Discharge standard of water pollutants for pulp and paper industry) that, the discharge limit of total nitrogen for pulping enterprises is 18 mg/L, the discharge limit of total nitrogen for waste paper pulping and papermaking enterprises is 15 mg/L, the discharge limit of total nitrogen for other pulping and papermaking enterprises is 15 mg/L, and the discharge limit of total nitrogen for papermaking enterprises is 15 mg/L. For another example, it is stipulated in GB 21904-2008 (Discharge standard of water pollutants for pharmaceutical industry, Chemical synthesis products category) that, the discharge limit of total nitrogen for existing enterprises is 50 (40) mg/L, and the discharge limit of total nitrogen for new enterprises is 35 (20) mg/L.
Current methods for effluent denitrogenation at home and abroad can be classified as physic-chemical methods and biological denitrogenation methods, wherein the physic-chemical methods include air stripping method, breakpoint chlorination method, zeolite adsorption method and flocculation sedimentation method. Both the air stripping method and the flocculation sedimentation method can be used for pretreatment of high-ammonia nitrogen effluent, but the latter is higher in operation costs. Both the breakpoint chlorination method and the zeolite adsorption method are suitable for advanced treatment, however, the former requires liquid chlorine which is too expensive and difficult to preserve, but it can compensate for the maladaptation of the stripping method to the cold season, and the treatment of the regenerated liquid remains a problem for the latter. Biological denitrogenation methods include the traditional process of denitrogenation based on three reactions of ammonification, nitrification, denitrification, A/O (anoxic/aerobic) denitrogenation process, oxidation ditch nitrification denitrogenation method and SBR (intermittent aeration activated sludge method). Biological methods for denitrogenation are in various forms, and have great potential due to their characteristics such as economy and absence of secondary pollution.
However, the above methods disclosed in the prior art cannot sufficiently utilize the carbon source in the original water to achieve the discharge requirements for denitrogenation treatment, and thereby require addition of more carbon source. With the development of economy and the increasing attention paid to the environment protection by countries, the discharge standard for total nitrogen is continuously increasing. For example, the US will implement a discharge standard of TN 5 mg/l from 2020, and the current treatment technologies cannot achieve the requirement of this discharge standard.